Results 1 to 7 of 7

Thread: How much extra capacitance can I use?

  1. #1
    Supporting Member
    Join Date
    Feb 2007
    Location
    Seattle WA
    Posts
    389
    Thumbs Up/Down
    Received: 22/0
    Given: 2/0
    Rep Power
    13

    How much extra capacitance can I use?

    I am working on an Ampeg J-12 amp that has a 40/20/20uf @450v multi-section can capacitor. I am considering changing it to one I have in my stash that is 40/40/40uf @450v. Should I use it?

    I know that transistor circuits require lots more power filter capacitance, especially in demand heavy circuits like bass amps. This is why transistor power supplies have hundreds or thousands of uf capacitance. I have been told that more capacitance on tube circuits can stress the rectifier tube, but the Ampeg amp has a solid state rectifier.

    So back to my original question. When is too much capacitance too much?

    0 Not allowed! Not allowed!

  2. #2
    Old Timer
    Join Date
    May 2006
    Location
    Chill-Ville, VA
    Posts
    2,976
    Thumbs Up/Down
    Received: 541/4
    Given: 982/9
    Rep Power
    16
    It's generally only a concern if you have a tube rectifier, and then only for the first capacitor in the line. Which model if Jet & rectifier do you have? It may slightly change the tone of the earlier stages, but that's subjective.

    Also, the specs on the vintage can were probably something like +80/-20% or vice versa. Meaning, it may not have been that far from what you have to begin with...

    Jusyin

    1 Not allowed! Not allowed!
    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

  3. #3
    Senior Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    1,478
    Thumbs Up/Down
    Received: 1,072/1
    Given: 674/2
    Rep Power
    4
    Quote Originally Posted by Axtman View Post
    I am working on an Ampeg J-12 amp that has a 40/20/20uf @450v multi-section can capacitor. I am considering changing it to one I have in my stash that is 40/40/40uf @450v. Should I use it?

    I know that transistor circuits require lots more power filter capacitance, especially in demand heavy circuits like bass amps. This is why transistor power supplies have hundreds or thousands of uf capacitance. I have been told that more capacitance on tube circuits can stress the rectifier tube, but the Ampeg amp has a solid state rectifier.

    So back to my original question. When is too much capacitance too much?
    Regarding rectifier stress it's only the first/main filter capacitor that matters. And it seems that would not change using your replacement.
    A general design analysis would mean evaluation of turn-on surge current and repetitive charging currents wrt. rectifier specs.

    1 Not allowed! Not allowed!
    - Own Opinions Only -

  4. #4
    Supporting Member
    Join Date
    Feb 2007
    Location
    Seattle WA
    Posts
    389
    Thumbs Up/Down
    Received: 22/0
    Given: 2/0
    Rep Power
    13
    Thanks Justin!

    I have the Ampeg J-12.
    Attached Files Attached Files

    0 Not allowed! Not allowed!

  5. #5
    Old Timer
    Join Date
    May 2006
    Location
    Chill-Ville, VA
    Posts
    2,976
    Thumbs Up/Down
    Received: 541/4
    Given: 982/9
    Rep Power
    16
    Cool, you have a SS rectifier. The reason I ascked was cuz there was the first J-12 I think in the 50s, then the J-12-A, B, D, & I believe D. I've gotva T with the extinct & unobtainium 6BK11s, subbed w. 6C10s (also nearly extinct & unobtainium.

    Justin

    0 Not allowed! Not allowed!
    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

  6. #6
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    11,288
    Thumbs Up/Down
    Received: 1,239/21
    Given: 3,135/8
    Rep Power
    22
    As far as transistor amps needing more capacitance, I think it's more that the high capacitance values are not available at the high voltage ratings needed for tube amps. At least not affordable ones.
    Even more so back when tubes were the norm for all electronics.

    1 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  7. #7
    Senior Member
    Join Date
    Mar 2018
    Location
    Germany
    Posts
    1,478
    Thumbs Up/Down
    Received: 1,072/1
    Given: 674/2
    Rep Power
    4
    As far as transistor amps needing more capacitance, I think it's more that the high capacitance values are not available at the high voltage ratings needed for tube amps.
    Smoothing quality (low ripple voltage) not only depends on filter capacitance but also on charging series resistance and and discharging current.
    SS amps generally are low impedance/higher current circuits. So for same smoothing they require much more filter capacitance than tube amps.

    3 Not allowed! Not allowed!
    - Own Opinions Only -

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. is capacitance capacitance?
    By daz in forum Music Electronics
    Replies: 34
    Last Post: 01-19-2015, 07:57 PM
  2. Extra gain stage from extra triode
    By Spitfireb in forum Mods & Tweaks
    Replies: 3
    Last Post: 11-04-2010, 07:33 PM
  3. Can you have too much filter capacitance?
    By Axtman in forum Theory & Design
    Replies: 11
    Last Post: 07-17-2009, 02:33 AM
  4. Replies: 4
    Last Post: 03-19-2009, 12:35 PM
  5. Stray capacitance???
    By MikeT in forum Maintenance, Troubleshooting & Repair
    Replies: 8
    Last Post: 07-12-2008, 01:05 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •